WO2001060588A1 - Method for making tubes by laser welding - Google Patents

Abstract

The invention concerns a method which consists in: (a) providing a strip (1), (b) guiding and rolling it to position the edges (2, 3) facing each other, (c) laser welding said edges, and compressing the welded edges, so as to form the tube, (d) feeding the tube at a speed V, and cutting longitudinally tube portions. Said method is characterised in that it consists: (1) in providing a strip material (1) having a bending strength ranging between 5 and 10 N measured by a method called support blade method; (2) first guiding it along the transverse axis Y using lateral guiding means; (3) rolling said strip, around a fixed central mandrel (62) with mobile transporting strip (620), by pushing back its edges (2, 3), considering said bending strength of said strip, so as to form a sealing cavity E; (4) directing towards said space E a laser beam (5) inputting at least half the amount of energy required to weld the edges (2) and (3); (5) compressing said edges by subsequently inputting the complementary energy required to obtain said amount of energy, so as to weld them and thus form said tube.

Description

 LASER SOLDERING TUBE MANUFACTURING PROCESS

FIELD OF THE INVENTION

The invention relates to the manufacture of tubes in the field of cosmetology, hygiene and pharmacy, tubes, typically made of plastic, formed by rolling a strip and by laser welding of the edges of the strip.

STATE OF THE ART

Conventional manufacture is already known, as typically described in patent FR 1 571 778, of tubes by rolling a strip and thermal welding, by induction, of the facing edges.

It is also known to form a tube and perform an axial weld of the edges by an energy contribution due to a beam of laser radiation. Thus, US Patent 4,540,392 discloses the formation of cardboard tubes typically coated with PE, rolling a strip and sending a laser beam between the flanges to be welded facing each other.

In European application No. 237 192, a device, such as a prism, is placed between the surfaces to be welded to reflect the laser beam on each of the surfaces to be welded. In German patent application No. 38 13 570, reflectors are used) outside ^the film to be welded to confine the laser beam in the material to be heated for welding.

PROBLEMS POSED A first problem of the known conventional methods for manufacturing tubes concerns the speed of manufacture: the known methods offer a typical production speed which peaks at 30 m / min.

In fact, in the conventional process, the production speed cannot be increased because, taking into account the nature of the materials involved and the thermal properties of these materials, in particular as regards heat transfer, it is not possible to heat / cool the edges to be welded faster.

In the laser welding process, it is not possible to increase the production rates under penalty of obtaining tubes having a weld if not defective, at least not reliable enough to constitute the basis of an industrial process.

A first object of the invention is a method making it possible to increase the production rate by at least 50%.

A second problem arises when a strip comprising a central layer of EVOH is used as a barrier material as the starting strip. Indeed, it is important in this case to have a process making it possible to obtain a tube whose welded edges mask or coat the central layer of EVOH sensitive to humidity.

DESCRIPTION OF THE INVENTION

According to the invention, in the process for manufacturing a tube, typically made of plastic, on a production line: a) a strip is supplied with said plastic, b) the strip is guided and it is rolled in order to looking at the edges of said strip, c) laser welding said edges according to a generatrix of said tube of axis of revolution X, typically cylindrical, and compressing the welded edges, so as to form said tube, d) driving said tube and said strip at a speed V, and, typically, portions of tubes of a predetermined length are cut to length, process characterized in that: 1) a strip material is supplied with a flexural strength, measured according to the so-called support blade method, ranging from 5 to 10 N,

2) before rolling of said strip, it is first guided along the transverse axis Y by means of a lateral guiding means, so as to guarantee a fixed lateral positioning of said strip relative to the long axis X of the tube,

3) said strip is rolled around a fixed central mandrel with a movable transport strip, pushing its edges, taking into account said resistance to bending of said strip, using rolling means, and typically towards the top, so as to bring the edges of the strip opposite, forming a sealing cavity or space E having, over a length L and in the plane Pyz perpendicular to the axis X, a section, typically triangular, variable with l 'abscissa 1 going from 0 to L, the top of said triangular section being formed by the junction of a so-called lower edge of the strip, of width lj between its outer end and its inner limit, or of its extension, with an edge said upper of the strip and of width l _s bounded by said junction, and the base AB of said section being bounded by said end A of said upper edge and by said inner limit B of said lower edge, the base AB being maximum for 1 = 0 e t typically zero, in C for 1 = L, so as to form a fixed space E whatever the speed V,

4) a laser beam (5) of a power adapted to the speed V is directed towards said space E, so as to bring, to the internal surface of said upper edge (2) constituting the upper face of said space and / or to the external surface of said lower edge (3) constituting the lower face of said space, at least half the amount of energy required to weld said upper (2) and lower (3) edges,

5) said upper and lower edges are compressed according to a longitudinal overlapping zone R, providing, typically by means of induction heating, any additional energy to obtain said quantity of energy, so as to weld and thus form said tube

In fact, the Applicant has analyzed in detail the reasons why the laser welding processes did not make it possible to obtain higher production speeds. Following the studies conducted by the applicant, in particular through analysis ^of images with a high speed camera, she found that the main reason for this failure lies in the relative instability of said space or cavity E, regarding its relative position with respect to a presumed fixed laser beam, instability which does not necessarily appear to the naked eye, so that by implementing the combination of means according to the invention, this relative instability is otherwise eliminated, from less reduced to a level low enough not to have harmful consequences on the quality of the longitudinal weld. The combination of means according to the invention comprises at least: - the selection of a starting material having a flexural strength between certain limits, insofar as, as observed by the applicant, the method according to the invention could not be applied to strip materials either too flexible (flexural strength less than 5 N), or too inflexible (flexural strength greater than 10 N) and, therefore, only concerns a range relatively narrow material, with a flexural strength of 5 to 10 N measured according to the method known as the support blade which will be explained in the examples and illustrated in FIG. 9.

- upstream of the rolling step, a lateral guiding means so that the median of the strip is and remains in the central plane XZ of the tube to be formed and of the device for forming this tube, a device which notably comprises a central mandrel on which the tape is rolled up,

means for rolling the strip, on a fixed mandrel, to bring the edges to be welded of the strip opposite and form an open space E between these facing edges, a space having the shape of a very elongated triangular pyramid, and in particular to ensure that this space E keeps a fixed position whatever the speed of the strip, - a supply of energy by laser beam to weld the facing edges, this supply being able to constitute only a majority fraction of the energy supply necessary to obtain a correct weld.

Indeed, according to the invention, it is preferable that the laser beam provides only part of the energy necessary for welding. In fact, the method of the invention, unlike the methods of the prior art, in no way implies the use of reflectors, any more than it requires multiple reflections of the beam between the edges to be welded, and favors direct attack of the beam on the edges to be welded, so as to locally raise the temperature of the surfaces to be welded, without taking the risk of melting the material constituting the strip.

This combination of means makes it possible to achieve all the objectives of the invention, as will appear in the detailed description and in the figures according to the invention.

DESCRIPTION OF THE FIGURES

All the figures relate to the invention.

Figure 1 is a view, in longitudinal section in the XZ or Pxz plane, of the device or production line (6) for manufacturing the tubes (4) or tube portions (41) from a strip (1) on reel.

Figures la to ld are sectional views along the plane Pxz of the various moving bands of the device (6).

Figure le and lf relate to the transformation of the material into a strip (1) in said line (6): figure le is a section in the Pxz plane, while figure lf is a series of cross sections in the YZ plane or Pyz.

Figure 2 is a sectional view in the Pyz plane of a device (631) for guiding the edges or selvedges (2,3) of the strip (1).

Figure 3 is a schematic view of a device (61) for tensioning the strip (1).

Figures 4a and 4b are sections in the plane P _γz which illustrate the rolling of the strip (1).

Figures 5a to 5c show the space or cavity E formed between the upper (2) and lower (3) edges facing each other, into which the laser beam will be directed. Figures 5a and 5b are views in the Pyz plane. while Figure 5c is a perspective view. Figures 6 to 6b relate to the irradiation of space E by the laser beam (5), the orientation of the beam being that of its bisector. FIG. 6 is a sectional view of the space E along the plane Pγ _Z , while FIGS. 6a and 6b illustrate the orientation of the beam and the meaning of the angles ai and α ₂ .

Figure 7 is a sectional view along the plane Pyz, of the device downstream of the abscissa point X _E of Figure lf.

Figure 8 is a sectional view along the Pyz plane, of the weld (42) of the tube.

Figure 9 is a perspective view schematically the method of measuring the flexural strength according to the so-called support blade method.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, said compression of the upper (2) and lower (3) edges which constitutes their union, can close, at C, the downstream end of said space E, so that the open face of said space E typically has the shape of a triangle ABC, the vertex C of which is located at the downstream end of said space E, as clearly appears in FIG. 5c.

It may be advantageous to maintain, over the entire length L of the space E, the end (30) of said lower edge (3) at a vertical dimension Z typically constant with respect to the central mandrel (62). Thus, it is easier to position the laser beam (5) and to irradiate at least the lower edge (3).

As illustrated in FIGS. 4a and 4b, it is possible to maintain, over said distance L, said lower edge (3) at a fixed vertical dimension Z, by means of one or more so-called "low" rollers (633) bearing on the lower edge (3) of said film or on a part (13), adjoining said edge (3), rollers which typically have a concave profile (6330) intended to cooperate with a convex profile of said central mandrel (62), and thanks to the flexural strength of said strip (1).

Preferably, and as illustrated in FIGS. 4a, 4b and 5c, the vertical dimension Z of the end (20) of said upper edge (2) gradually decreases over said distance L, when 1 goes from 0 to L, thanks to a or several so-called "high" rollers (632) bearing on the upper edge (2) of said film or on a part (12), adjoining said edge (2), rollers which have a concave profile (6320) typically intended for cooperate with a convex profile of said central mandrel (62), and by virtue of the flexural strength of said strip (1).

According to the invention, in step 2) of the method, said lateral guide means (60) can comprise means, typically provided with a photoelectric cell (600), for continuously determining the position of said strip on the through axis Y, and to correct any deviation so that the median plane (10) of said strip (1) contains said axis X. This lateral guide means (60) typically comprises two spaced parallel rollers, oriented along the Y axis and which can be offset from the Y axis by slight rotation along an axis oriented parallel to the Z axis, to correct a deviation in the lateral positioning of the strip, this offset being controlled by the deviation of the lateral positioning of the strip , which can be identified by one or more photoelectric cells, as shown diagrammatically in FIG. 3.

It is also possible, in substitution for the preceding means or in addition to the preceding means, to supply said strip (1) with a width greater than 1 to 5% than the theoretical width of said strip taking into account the diameter of the tube to be manufactured and a covering the edges to be welded, and, in step 2) of the method, cutting, typically by a pair of circular knives (601) positioned symmetrically with respect to the median or the median plane (10) of the strip, the excess width of said strip (602), so as to provide a strip whose median does not deviate from the centered plane P z containing the axis X. This mode has also been shown in FIG. 3. It is advantageous, in particular so as to be able either to widen the possibilities of supplying strips, or to increase the speed V while guaranteeing the quality of the weld (42) of the tube, to pass said film between tension rollers (61) , typically just upstream of step 2) of the method, to exert a tension in the long direction of the strip, tension typically lower than the elastic limit of the strip, but high enough for any undulations to disappear (15) edges or edges of said strip, undulations generally formed in a Pxz plane. Said tension can be exerted using two rollers or cylinders, with a downstream roller (611) imposing on said film an instantaneous linear speed greater than that imposed by an upstream roller (610). FIG. 3 represents the case where this tension is obtained by a different speed of rotation for the tension rollers (610,61 1) of the same diameter but with ω> coi. The same effect can be obtained with similar means.

Once a correct lateral positioning of the strip is ensured, that is to say when the median (10) of the strip is in the centered plane Pxz plane passing through the axis (40) of the tube or of the mandrel central (62), one begins to roll said strip. Thus, between step 2) of the method where the lateral positioning Y of the strip is regulated, and step 3) where said strip is rolled, an intermediate curved shape is imposed on said strip, typically by the cooperation of a central caster (630) in vertical abutment on the center line (10) of said strip, and at least one set of two lateral grooved castors (6310), typically those of a selvedge guide (631), exerting an action contrary tending to raise the edges or selvedges (2,3) of said strip, the angle of the two edges or selvedges being typically between 120 and 60 ° at this stage of the rolling step. The roller (630) is shown in Figure 1, while a selvedge guide (631) with two grooved rollers (6310) is shown in Figure 2.

As regards the laser beam (5) used in the invention, it can be oriented in the horizontal plane YX in a direction Dj making an angle oci between - 30 ° and + 90 °, relative to the transverse axis Reference Y, as illustrated in Figure 6a. This laser beam (5) can be oriented in the vertical plane ZDi, comprising said direction Di, in a direction D ₂ making an angle α ₂ between + 10 ° and -30 °, relative to the horizontal direction Dt, as illustrated in Figure 6b. As illustrated in FIG. 6, it is possible to choose for the laser beam (5) a focusing such that the focal point (50) is external to said cavity E, and so that the whole of the beam penetrates into said cavity E, the width (51) of the beam (5) at the entrance to said cavity E is typically between 0.9. AB and 0.3. AB.

The laser beam (5) can be oriented so as to provide energy in particular towards the apex S of said triangular section or towards said junction (16) located in the part (12) adjoining the upper edge (2), so that a protective rim (420) is formed and covers the inner edge (33) of said lower edge (3), typically by creep of the material of said upper edge (2). As already mentioned and as shown in Figures 5a and 5c, the vertex S corresponds to the junction line (16) between the upper edge (2) and the end (30) of the lower edge (3) or its extension.

Similarly, the laser beam (5) can be oriented so as to provide energy in particular towards the inner limit (31) of the lower edge, on said edge (3) or on said part (13) adjoining said edge, according to the position of the end (20) of the upper edge after rolling, so that a protective rim (420) is formed and covers the outer edge (23) of said upper edge (2), typically by creep of the material of said lower edge (3).

Thus, it is possible, as illustrated in FIG. 8, to form a weld (42) of the edges (2) and (3), the edges of which, denoted respectively (32) and (33), are protected by material. coming from the outer layers (14).

According to one embodiment of the invention, the laser beam (5) can be oriented in a predetermined direction Di and be oriented in a direction D ₂ , variable either by the angle α ₂ or by the dimension Z, direction regulated so as to that said beam is typically maintained in said space E. Thus, for example, said laser beam (5) can be maintained in space E either by modifying the focal distance of the beam, or by moving the laser. The laser beam (5) can be oriented in a direction Di with an angle _\ of between + 75 ° and + 90 °.

It may be advantageous to orient said laser beam (5) along the bisector of the angle β formed by said upper and lower edges, with the angle ai between -20 ° and + 20 °. In this case, the beam, which is almost perpendicular to the direction X of the strip or of the tube, is positioned near the base AB of the triangle ABC where the spacing between the edges (2) and (3) is maximum.

According to one embodiment of the invention, said laser beam (5) can be subjected to a scanning from front to back, in the direction X, over all or part of the distance L, at a scanning speed typically twice the speed. V, so that each portion of the upper (2) and lower (3) edges intended to receive said beam, receives it twice before compression of said edges, and so as to favor the absorption at the surface of the laser radiation. According to the invention, the energy of the laser beam is chosen at a level allowing its absorption by the material constituting the strip when the beam enters the space or the cavity E. This laser beam (5) can be introduced into said space through one or more optical fibers.

It is advantageous for said strip (1), before welding, to be kept under tension, in the direction X of the strip or of the tube, between 0.2 and 0.8 times its elastic limit. In fact, as observed by the applicant, this contributes to stabilizing the position of space E, even at high speed V.

According to an advantageous embodiment of the invention, in step 5) of the process, said upper (2) and lower (3) edges can be compressed with a thermal contribution, typically obtained with induction heating (641) which completes the prior heating of said edges (2,3) by the laser beam (5). Indeed, although the laser beam can bring to the edges to be welded all the necessary energy, it is preferable that this energy supply is made on the one hand by a first supply by a laser beam on the edges to be welded themselves. same, and on the other hand by a additional contribution during the compression of the edges to be welded facing each other, this contribution being made by induction heating the "hot" movable strip (640) of steel coated with Teflon.

The Applicant has observed that the best performance is obtained by using this double energy supply, the first taking place inside the weld, the second outside the weld. In particular, it is thus possible to obtain the best performance both with regard to the production speed and the protection of the edges (23,33) of the edges (2,3) when such protection is necessary, which does not This is not always the case since only the most demanding applications use a strip comprising an inner layer of EVOH.

In the method according to the invention, at the end of step 5), the longitudinal weld (42) formed between said upper (2) and lower (3) edges can be cooled, so as to be able to increase the speed V A “cold” moving strip (650) can be used for this.

It is also possible to join the two bands (640) and (650) into one, as indicated by dotted lines between FIGS. 1b and 1c, in particular in the case where the additional supply of energy is not very Student.

In the method according to the invention, the ranges can be chosen for the parameters relating to the space E and to the weld (42): With regard to the space E:

- L: typically between 5 and 20 cm

- AB: typically between 1 and 8 mm - Width l _s and 1, edges: typically between 1 and 8 mm With regard to welding (42):

- Covering R of the edges to be welded: typically between 0.5 and 3 mm

- Width of the protective rim (420), if applicable: typically between 0.5 and 2 mm. According to the invention, the strip (1) can be made up or comprise the following materials for implementing the process of the invention: PE, PP, PA, PET, EVOH, or other plastics with barrier properties or not, plastic or metalloplastic multilayer materials externally coated with the above-mentioned thermoplastic layers, materials which may comprise deposits of SiO _x , of carbon in thicknesses typically between 150 and 400 μm. These materials are typically printed on one side.

As an example of a multilayer material, mention may be made of a material having the following structure: PE / EVOH / PE. As an example of a metalloplastic material, mention may be made of PE / M / PE, where M denotes a metal sheet, typically Al, Fe, Cu, etc.

It is also possible to have plastic multilayer materials comprising a layer of paper: PE / Paper / PE

As already mentioned, these materials must have a flexural strength in the range 5N - 10 N. Indeed, it is thanks to these mechanical properties of the strip that it is possible to compare the edges to be welded without having to introduce positive guidance of these edges themselves, and thus that it is possible to send a laser beam into a strictly absorbent medium consisting of the material to be welded only.

Another object of the invention consists of the device (6) for implementing the method according to any one of claims 1 to 26 comprising:

- lateral guide means (60) of the strip (1),

- rolling means (63) of the strip around a fixed central mandrel (62), so as to compare the edges to be welded (2,3) and to form a fixed cavity or space E, closed to its downstream end by the overlap R of said edges forming the start of the longitudinal weld (42),

a laser (5) for heating the interior surfaces of the edges (2, 3) to be welded by directing a laser beam into said cavity E,

- a means (64) for compressing said overlap of the edges forming the weld, typically by means of a metal strip (640), with a supply of energy complementary to that of the laser, typically by induction heating (641) of said metal strip,

a means (65) for cooling said covering, typically by means of a metal strip (650),

- a cutting means (67) for cutting the tube (4) into tube portions (41),

- means for positioning and moving the tube (4),

means, typically computer, for controlling the line comprising sensors measuring quantities, typically speed, position of the edges of the strip, temperature, and actuators for maintaining the set values of said quantities within a range of values predetermined.

EXAMPLES OF REALIZATION

The material used was a PE / Adh / EVOH / Adh / PE strip, where PE, Adh and EVOH respectively denote a layer of PE, adhesive and ENOH. The respective thicknesses of the layers of the strip being: 150 μm, l Oμm, 20 μm, lOμm and 90 μm. This strip, taking into account the choice of materials and their thickness, has a flexural strength of 6.6 Ν.

The measurement of the flexural strength is carried out according to the so-called support blade method, shown diagrammatically in FIG. 9: the head of a traction device (7), not shown, is provided with a blade (70 ) typically triangular, the base of which measures 13.3 mm in length. The maximum bearing force is measured on a portion of cylindrical tube made of the material to be tested, force necessary to bend the top of the cylinder by 20 mm, as shown in dotted lines in FIG. 9, the portion of tube being placed in a square section plinth having the inside diameter of the outside diameter of the tube, chosen equal to one inch, or approximately 25.5 mm.

The figures constitute an exemplary embodiment. Figure 1 is a view, in longitudinal section in the XZ or P z plane, of the device or production line (6) for manufacturing the tubes (4) or tube portions (41) from a strip (1 ) on reel.

We have identified different means of line (6) in the longitudinal direction X by their abscissa X = X _A to X _F in FIG.

Figures la to ld are sectional views along the Pxz plane of the various moving bands of the device (6) closed on themselves, positioned relative to each other along the X axis, but offset along the Z axis of so as to present them separately

- Figure la: strip (620) integral with the central mandrel (62), shown in section in Figures 4az, 4b and 7, located below the longitudinal weld (42), and extending from X = X _D to X = X _G either over a length of approximately 1.8 m.

- figure lb: "hot" compression strip (640), located above the longitudinal weld (42) from X = X _E to X = XF, i.e. over a length of approximately 0.4 m - figure le: strip "cold" compression (650), located above the longitudinal weld (42) from X = X _F to X = XG, ie over a length of approximately 1 m in FIG. 1 c,

- Figure ld: support strip (660), located below the rolled strip and the tube, driving the tube over a length of about 2.5 m, between X = X _B to X = X _H , Figure le and lf relate to the strip material (1) in said line (6) and to its transformation by rolling: the figure shows this transformation in section in the plane Pxz, while FIG. lf illustrates, in the form of cross sections in the YZ or Pγ _Z plane, the different stages of rolling the strip (1) at different stages of the process or, which comes to the same thing, different abscissas, denoted from X _A to X _H along the X axis.

In what follows, relative to FIG. 1, we will indicate, from upstream to downstream, the various means present on the line (6), in addition to the various bands of FIGS. 1a to 1c, some of these means not being not shown as such in Figure 1 so as not to weigh it down: - upstream of X = X _A , which represents the point of the line (6) where the strip arrives flat and in the correct transverse position, that is to say with its median plane (100) comprising the longitudinal axis ( 40) fixed, there are first the means (10) for supplying the strip (1), typically a reel of material reel, then a lateral guide means (60), then, as illustrated in more detail on FIG. 3, two tension rollers (61), with an upstream tension roller (610) and a downstream tension roller (61 1), the difference in rotational speed of which induces tension in the strip intended to stabilize its edges or strands by removing lateral undulations when present. Figure 3 is a schematic view of a device (61) comprising two tension rollers (610) and (611), with either, the two rollers being of the same diameter as illustrated in Figure 3, the second roller (61 1 ) rotating at an angular speed ω ₂ greater than that of the first roller (610), ie, the angular speeds being close, the second roller (611) having a larger diameter than the first roller (610), so that that the linear speed of the strip (1) is higher at the outlet of the second roller than of the first roller, and that as a result, the strip (1) is subjected between these two rollers to a longitudinal tension which can reach the elastic limit of the material constituting the strip.

The strip (1) has been shown upstream of the roll (610) with irregularities or undulations of the edges, whereas, after tensioning of the strip, downstream of the roll (61 1), the strip has no edges irregular. This tension, typically between 0.3 and 0.8 times the elastic limit of the material forming the strip (1), is maintained during the formation of the tube (4).

- between X = X _A and X-XR, there are complementary positioning means, such as those shown in FIG. 3.

- At point X = X _R , there is a central caster (630) bearing on the strip (1), so as to start rolling this strip along a transverse profile shown in Figure 1 f.

- At point X = Xç, there are the grooved rollers (6310), the strip then having a transverse profile shown in Figure lf. FIG. 2 represents, in section in the Pγ _Z plane. a device (631) for guiding the edges or selvedges (2,3) of the strip (1), using two grooved rollers (6310), the edges being held in the grooves, this device (631) comprising a circular support (631 1) itself fixed to the frame of the line (6).

des galets de roulage haut (632) et bas (633) (non représentés sur la figure 1) sont appliqués latéralement, comme représenté sur les figures 4a et 4b, de manière à rabattre les bords (2,3) de la bande et former la cavité ou espace E, de géométrie constante prédéterminée, comme illustré sur les figures 5a à 5c et sur la figure 6. Un faisceau laser (5) est introduit dans la cavité E, comme représenté sur la figure 6, avec une orientation selon les figures 6a et 6b.- Between X = X and X = Xn, there are in particular means (not shown in FIG. 1) for holding the central mandrel (62) in position and possibly for continuing the rolling of the strip.

top (632) and bottom (633) rollers (not shown in Figure 1) are applied laterally, as shown in Figures 4a and 4b, so as to fold the edges (2,3) of the strip and form the cavity or space E, of predetermined constant geometry, as illustrated in FIGS. 5a to 5c and in FIG. 6. A laser beam (5) is introduced into the cavity E, as shown in FIG. 6, with an orientation according to the Figures 6a and 6b.

A CO ₂ laser of the ROFIN SINAR (R) brand was used, either of the SC20 type and of a power of 250W making it possible to work in a speed range going from 20 to 30 m / min, or of the SC60 and a power of 600W allowing to work in a speed range up to 60 m / min.

FIGS. 4a and 4b are sections in the plane P _γz which illustrate the rolling of the strip (1) using “low” (632) and “high” (633) rolling rollers, rollers which respectively have a concave surface (6320) and (6330) and an axis of rotation

(6321) and (6331), so as to compare the upper (2) and lower (3) edges with a view to their welding.

The axes (6321) and (6331) are vertical in Figure 4a, and inclined in Figure 4b. 5a to 5c show ^the space or cavity E formed between the upper edges (2) and bottom (3) placed opposite, wherein the laser beam will be directed.

FIGS. 5a and 5b are views, in the Pyz plane, of the ends of the zone of action of the laser, zone of length L marked by the abscissae, X _D and X _E , of its ends, the edges (2,3 ) making an angle β typically between 15 and 70 ° for the abscissa X = X _D , at the upstream end of this zone, and a virtually zero angle for the abscissa

X = X _E at the downstream end of this zone. FIG. 5c represents, in perspective, the entire space or cavity of length L, the upstream end of which is represented in FIG. 5a and the downstream end in FIG. 5b. Figures 6 to 6b relate to the irradiation of space E by the laser beam (5), the orientation of the beam being that of its bisector. FIG. 6 is a sectional view of space E along the plane Pyz, while FIGS. 6a and 6b illustrate the orientation of the beam and the meaning of the angles ai and α ₂ . at point X = Xκ, the longitudinal weld (42) begins, the edges (2,3) then being folded over one another, after the facing interior surfaces have been brought to the appropriate temperature by the laser beam , as shown in Figure 1 f. - between X = X _g and X = X _F , the hot strip (640) compresses the longitudinal weld, as illustrated in FIG. 7. This strip was heated by induction, to a temperature between 130 ° C and 170 ° C according to speed V.

Figure 7 is a sectional view along the Pyz plane, of the device downstream of the abscissa point X _E of Figure lf, the different elements being shown apart for clarity of the figure, with the central mandrel in the center (62 ) carrier of the strip (620) on which the tube (4) is rolled. The weld (42) of the tube is compressed between an upper strip (641) and a lower strip (620), a heating means (640) - typically by induction - and compression (64) being shown above the strip upper (641).

- between X = X _F and X = Xr „the cold strip (650) compresses and cools the longitudinal weld.

- downstream of point X = X _G , the tube (4), formed, is no longer held by an internal mandrel (62), but by lateral rollers (not shown) which guide the tube (4) towards a device cutting (67) to obtain tube portions (41) of predetermined length.

The line (6) comprises means (not shown) for controlling the computerized line comprising the necessary sensors relating in particular to the positioning of the strip before rolling, to the speed of the different parts of the line, to the temperature of the weld and of the heating means used, with the energy of the laser beam, and the corresponding actuators to maintain the set values within a predetermined interval.

The tests were carried out at a whole series of different speeds: 20 - 30 - 40 - 45 - 50 - 55 and 60 m / min.

In the previous tests, the share of energy provided by the laser and that provided by induction heating was considered as a first approximation (to the nearest loss) as being proportional to the installed power. Thus, the tests were carried out with an energy supply close to 3/4 by the laser and 1/4 by induction. Other tests have shown the possibility of varying, around these values, the share of heating by laser and that of heating by induction.

At each test, the tubes obtained were examined in section, as illustrated in FIG. 8 which is a sectional view along the plane P _γz , of the weld (42) of the tube. The central layer (11), typically made of EVOH, is covered with external layers (12), typically made of polyolefin plastic, the formation of the weld according to the invention leading to the material of the external layers (12) flowing. and forms a protective rim (12) which isolates the central layer (11).

Tubes were obtained having the following values (determination on sections) for:

* the covering R: 1, 5 mm * the width 1, over which the lower edge is covered by the upper edge with its creep zone forming the protective rim (420) is substantially equal to the corresponding width l _s and is worth approximately 3 mm, so that the inner layer of EVOH is protected by the protective edges (420).

Depending on the speed V, the following observations were made with regard to the line conduct and the quality of the tube obtained, mainly the quality of the weld

: beyond a speed V equal to 50 m / min, the integrity of the weld is no longer obtained, while below a speed V equal to 50 m / min, the weld is perfectly cohesive and does not delaminate.

ADVANTAGES OF THE INVENTION The invention discloses a process having several advantages:

on the one hand, the method makes it possible to significantly increase the speed of manufacture of the tubes,

on the other hand, this process can use a very wide variety of strip materials, provided that these strip materials satisfy the conditions defined in the present invention,

- In addition, this process, which typically uses a double energy supply, both by a laser, and by an additional heating means, typically by induction, has great flexibility in operating the line, in particular in the event of variations in speed, or during starts or stops,

- in addition, the double energy input leads to good quality and constant quality welding, in particular as regards the covering of the wafers protecting the central layer of EVOH,

- Finally, this process can be implemented by means of relatively inexpensive transformations of traditional production lines.

List of landmarks

Strip / strip material 1

Coil / strip feed 10 Longitudinal / median median plane ... 100

EVOH 11 central layer

Part adjoining the upper edge 12

Part next to lower edge 13

Outer layer 14 Ripples on the edges 15

Junction of end 30 and edge 2 ... 16

Upper edge 2

End 20

Inner boundary 21 Part adjoining the edge (2) 22

Upper edge of the weld 23 Bottom edge 3

End 30

Inner limit 31

Part adjoining the edge (3) 32 Upper edge of the weld 33

Tube 4

X axis of tube or central mandrel 62 40

Tube portions 41

Longitudinal weld 42 Protective edge 420

Laser beam 5

Focal point 50

Device / production line 6

Lateral guide means 60 Photocell 600

Circular knives 601

Excess width 602

Tension rollers 61

Upstream roller (coi) 610 Downstream roller (ω ₂ ) 61 1

Central chuck 62

Mobile conveyor belt 620

Driving resources 63

Central caster 630 Edge guide 631

Throat Casters 6310

Support 631 1

Rollers high 632

Concave profile 6320 Rotation axis 6321

Low rollers 633 Concave profile 6330

Rotation axis 6331

Compression media 64

"Hot" moving belt 640

Induction heating 641

Cooling media 65

"Cold" mobile belt 650

Support means 66

Support strip 660

Pipe cutting device 67

Traction device 7

Support blade 70

Base 71

Claims

1. Method for manufacturing a tube (4), typically made of plastic, on a production line (6), in which: a) a strip (1) is supplied with said plastic, b) said strip is guided and it is rolled to bring the edges (2, 3) of said strip opposite, c) said edges are laser welded along a generatrix of said tube of axis of revolution X, typically cylindrical, and the welded edges are compressed, so as to form said tube, d) driving said tube and said strip at a speed V, and, typically, portions of tubes (41) of a predetermined length are cut to length, process characterized in that: 1) a strip material (1) is supplied with a flexural strength, measured according to a method called the support blade, ranging from 5 N to 10 N, 2) before rolling of said strip, it is first guided along the transverse axis Y by means of a lateral guiding means (60), so as to guarantee a fixed lateral positioning of said strip relative to the long axis X (40) of the tube, 3) said strip is rolled around a central mandrel (62) fixed to a mobile transport strip (620), pushing its edges (2,3), taking into account said resistance to bending of said strip, at the using rolling means (63), and typically upwards, so as to bring the edges (2, 3) of the strip opposite, forming a sealing cavity or space E having, over a length L and in the Pyz plane perpendicular to the X axis, a section, typically triangular, variable with the abscissa 1 going from 0 to L, the vertex S of said triangular section being formed by the junction (16) of a so-called lower edge ( 3) strip, width 1; between its outer end (30) and its inner limit (31), or its extension, with a so-called upper edge (2) of the strip and of width l _s between its outer end (20) and said junction (43), and the base AB of said section being bounded by said end A (21) of said upper edge (2) and by said inner limit B (31) of said lower edge (3), the base AB being maximum for 1 = 0 and typically zero, in C for 1 = L, so as to form a fixed space E whatever the speed V, 4) a laser beam (5) of a power adapted to the speed V is directed towards said space E, so as to bring, to the internal surface of said upper edge (2) constituting the upper face of said space and / or to the external surface of said lower edge (3) constituting the lower face of said space, at least half the amount of energy required to weld said upper (2) and lower (3) edges, 5) said upper and lower edges are compressed according to a longitudinal overlapping zone R, providing, typically by means of induction heating, any additional energy to obtain said quantity of energy, so as to weld and thereby form said tube. 2. Method according to claim 1 wherein said compression of the upper (2) and lower (3) edges which constitutes their union, closes at C the downstream end of said space E, so that the open face of said space typically has the shape of a triangle ABC whose vertex C is located at the downstream end of said space E. 3. Method according to any one of claims 1 to 2 wherein, over the entire length L of the space E, the end (30) of said lower edge (3) is maintained at a vertical dimension Z typically constant relative to the mandrel central (62). 4. Method according to claim 3 wherein, over said distance L, said lower edge (3) is maintained at a fixed vertical dimension Z, by virtue of one or more so-called "low" rollers (633) bearing on the edge lower (3) of said film or on a part (13), adjoining said edge (3), rollers which have a concave profile (6330) typically intended to cooperate with a convex profile of said central mandrel (62), and thanks to the resistance when said strip (1) flexes. 5. Method according to any one of claims 1 to 4 wherein, over said distance L, the vertical dimension Z of the end (20) of said upper edge (2) gradually decreases when 1 goes from 0 to L, thanks to one or several so-called rollers "Tops" (632) bearing on the upper edge (2) of said film or on a part (12), adjoining said edge (2), rollers which have a concave profile (6320) typically intended to cooperate with a convex profile of said central mandrel (62), and thanks to the flexural strength of said strip (1). 6. Method according to any one of claims 1 to 5 wherein, in step 2) of the method, said lateral guide means (60) comprises means, typically provided with a photoelectric cell (600), for continuously determining the position of said strip on the Y axis, and to correct any deviation so that the median plane (10) of said strip (1) contains said X axis. 7. Method according to any one of claims 1 to 6 wherein, in step 1) of the method, we supply said strip (1) with a width greater than 1 to 5% than the theoretical width of said strip taking into account the diameter of the tube to be manufactured and of an overlap of the edges to be welded, and in which, in step 2) of the method, one cuts, typically by a pair of circular knives (601) positioned symmetrically with respect to the median or in the median plane (10) of the strip, the excess width of said strip (602), so as to provide a strip whose median does not deviate from the centered Pxz plane containing the X axis. 8. Method according to any one of claims 1 to 7 wherein, in particular so as to be able either to widen the possibilities of supplying strips, or to increase the speed V while guaranteeing the quality of the welding (42) of the tube, pass said film between tension rollers (61), typically just upstream of step 2) of the method, to exert a tension in the long direction of the strip, tension typically lower than the elastic limit of the strip, but fairly high so that possible undulations (15) of the edges or edges of said strip disappear, undulations generally formed in a plane Pxz. 9 The method of claim 8 wherein said tension is exerted using two rollers or cylinders, with a downstream roller (611) imposing on said film an instantaneous linear speed greater than that imposed by an upstream roller (610) 10 A method according to any one of claims 1 to 9 wherein between step 2) of the method where the lateral positioning Y of the strip is regulated, and step 3) where said strip is rolled, said strip is imposed on a form intermediate curved, typically by the cooperation of a central caster (630) in vertical abutment on the center line (10) of said strip, and at least one set of two lateral grooved casters (6310), typically those of a selvedge guide (631), exerting a contrary action tending to raise the edges or selvedges (2,3) of said strip, the angle of the two edges or selvedges being typically between 120 and 60 ° at this stage of the step rolling 11 Method according to any one of claims 1 to 10 wherein the laser beam (5) is oriented in the horizontal plane YX in a direction Di making an angle ai between - 30 ° and + 90 °, relative to the transverse axis Reference Y 12 The method of claim 11 in the laser beam (5) is oriented in the vertical plane ZDj, comprising said direction Dj, in a direction D ₂ making an angle α ₂ between + 10 ° and -30 °, relative to the horizontal direction Dj 13 Method according to any one of claims 1 to 12 wherein one chooses for the laser beam (5) a focus such that the focal point (50) is external to said cavity E, and so that the entire beam enters said cavity E, the width (51) of the beam (5) at the entrance to said cavity E is typically between 0.9 AB and 0.30 AB 14 A method according to any one of claims 1 to 13 in which the laser beam (5) is oriented so as to provide energy in particular towards the vertex S of said triangular section or towards said junction (16) located in the part (12 ) adjoining the upper edge (2), so that a protective rim (420) is formed and covers the inner edge (33) of said lower edge (3), typically by creep of the material of said upper edge (2). 15. Method according to any one of claims 1 to 14 wherein the laser beam is oriented (5) so as to provide energy in particular towards the inner limit (31) of the lower edge, on said edge (3) or on said part (13) adjoining said edge, according to the position of the end (20) of the upper edge after rolling, so that a protective rim (420) is formed and covers the outer edge (23) of said upper edge ( 2), typically by creep of the material of said lower edge (3). 16. Method according to any one of claims 1 1 to 15 in which the laser beam (5) is oriented in a predetermined direction D] and is oriented in a direction D, varying either by the angle or by the dimension Z, regulated direction so that said beam is typically maintained in said space E. 17. The method of claim 16 wherein said laser beam (5) is maintained in space E either by changing the focal distance of the beam, or by moving the laser. 18. Method according to any one of claims 1 1 to 15 wherein the laser beam (5) is oriented in a direction Dj of angle oti between + 75 ° and + 90 °. 19. Method according to any one of claims 11 to 15 wherein said laser beam (5) is oriented along the bisector of the angle β formed by said upper and lower edges, with the angle ai between -20 ° and +20 °. 20. Method according to any one of claims 1 1 to 15 in which said laser beam (5) is subjected to a scanning from front to back, in the direction X, over all or part of the distance L, at a scanning speed. typically double the speed V, so that each portion of the upper (2) and lower (3) edges intended for receive said beam, receive it twice before compression of said edges, and so as to favor the absorption on the surface of laser radiation. 21. A method according to any one of claims 1 to 20 wherein said laser beam (5) is introduced into said space through one or more optical fibers. 22. A method according to any one of claims 8 to 21 wherein said strip (1), before welding, is maintained under a tension between 0.2 and 0.8 times its elastic limit. 10 23. Method according to any one of claims 1 to 22 in which, in step 5) of the method, said upper (2) and lower (3) edges are compressed with a thermal contribution, typically obtained with induction heating (641 ) which completes the preheating of said edges (2,3) by the laser beam (5). 15 24. Method according to any one of claims 1 to 22 in which, at the end of step 5), the longitudinal weld (42) formed between said upper (2) and lower (3) edges is cooled, so as to ability to increase speed V. 25. Method according to any one of claims 1 to 24 in which the length L of the space E is between 5 and 20 cm, the length of its base AB is between 1 and 8 mm, the width l _s and lj edges being between 1 and 8 mm. 26. The method of claim 25 wherein the weld (42) has an overlap R of width between 0.5 and 3 mm, and a protective edge (420) of width between 0.5 and 2 mm. 27. Method according to any one of claims 1 to 26 in which the strip (1) is made up or comprises the following materials for implementing the method of J 0 the invention: PE, PP, PA, PET, EVOH, or other thermoplastic materials with barrier properties or not, coated plastic or metalloplastic multilayer materials externally of the previously mentioned thermoplastic layers, materials which may comprise deposits of SiO _x , of carbon in thicknesses typically between 150 and 400 μm. 28. Device (6) for implementing the method according to any one of claims 1 to 27 comprising: - lateral guide means (60) of the strip (1), - rolling means (63) of the strip around a fixed central mandrel (62), so as to compare the edges to be welded (2,3) and to form a fixed cavity or space E, closed to its downstream end by the overlap R of said edges forming the start of the longitudinal weld (42), a laser (5) for heating the interior surfaces of the edges (2, 3) to be welded by directing a laser beam into said cavity E, a means (64) for compressing said overlap of the edges forming the weld, typically by means of a metal strip (640), with a supply of energy complementary to that of the laser, typically by induction heating (641) of said metal strip, - a means (65) for cooling said covering, typically by means of a metal strip (650), - a cutting means (67) for cutting the tube (4) into tube portions (41), - means for positioning and moving the tube (4), means, typically computer, for controlling the line comprising sensors measuring quantities, typically speed, position of the edges of the strip, temperature, and actuators for maintaining the set values of said quantities within a range of values predetermined.